Changes in mental health in the German child and adolescent population during the COVID-19 pandemic – Results of a rapid review

Background This rapid review examines changes in the mental health of the German child and adolescent population during the COVID-19 pandemic. Methods The basis are 39 publications, which were identified by means of systematic literature search (until 19.11.2021) and manual search. The databases of the included publications were systematized with regard to their representativeness for the general population, and the indicators used were categorized with regard to the depicted constructs and their reliability. Results The large majority of the studies took place at the beginning of the pandemic until the summer plateau 2020. Representative studies mainly reported high levels of pandemic-related stress, increases in mental health problems, and negative impacts on the quality of life. Non-representative studies showed mixed results. Vulnerable groups could only be identified to a limited extent. Both routine and care-related data showed declines in the outpatient and inpatient service utilisation during the various waves of the pandemic followed by catch-up effects. Children and adolescents turned out to be more vulnerable during the pandemic compared to adults, but their stress levels varied with the waves of the pandemic and the related containment measures. Conclusions A future forward-looking crisis and pandemic management requires a close-knit and continuous surveillance of the mental health of children as well as an improved identification of risk groups.


Introduction
The beginning of the COVID-19 pandemic presented unprecedented challenges to the societies worldwide. In Germany, far-reaching non-pharmaceutical containment measures were introduced in mid-March 2020, shortly after ground, as well as children with pre-existing mental disorders appeared particularly affected [4]. After almost two years and three additional waves of the pandemic, a new review of the literature on the population-based mental health of children and adolescents in Germany during the pandemic seemed appropriate. Thus, this paper aims at a systematic synthesis of evidence according to the methodology of a rapid review. As in a systematic review, in a rapid review the evidence is systematically synthesised, however more quickly, using methodological 'shortcuts' [11,12].
In an abruptly occurring major health crisis, such as the current pandemic, authorities need quick and reliable data both about vulnerable population groups and the level of care they need [12] in order to be able to initiate measures effectively and quickly. Thereby, it is important that the data be generalisable to the general population [12,13]. Ad-hoc conducted online surveys using self-recruiting convenience samples via the internet, social media, or mouth-to-mouth propaganda can be used best to generate information quickly and cost-effectively. However, such studies are rarely population-representative and thus subject to the risk of bias with regard to the assessment of prevalences and/or time trends. In the case of surveys focussing on psychosocial stress, for example, individuals who acutely feel stressed may be particularly motivated to participate and may thus be overrepresented in the sample [14]. Vice versa, individuals with manifest mental disorders, older people, as well as individuals with low education tend to participate less likely in online surveys [12]. In studies using convenience samples, systematic non-participation of specific population subgroups cannot be compensated by means of weighting.
schools. Due to their specific developmental vulnerability, children and adolescents were particularly affected by many of these measures, which initially served in particular to protect older or chronically ill individuals [2,3]. For instance, the closures of day-care centres and of schools resulted in educational restrictions, loss of daily routine, or lack of or limited physical activity. Leisure activities, social and family contacts to grandparents, relatives, and friends were likewise restricted. Forced proximity due to the containment measures and/or pandemic-related economic difficulties in the families increased the risks for familial tensions and disputes and presumably also for domestic violence and child abuse and neglect [4]. Children and adolescents were also reported of being afraid of an own COVID-19 infection or the infection of a close family member (parents, grandparents) or their illness or death [5,6].
Putative impacts of the pandemic as well as impacts of non-pharmacological containment measures on the population mental health had been addressed in the international literature right from the start, more specifically, however, for adults than for children and adolescents [7][8][9][10]. In December 2020, Schlack et al. [4] presented a non-systematic, narrative literature review on the mental health of children and adolescents during the pandemic. It combined respective data and empirical results from the first pandemic wave for Germany until July 2020. At that point, however, these results were often only available as advance notifications or as press reports or press releases. These first findings suggested a high level of pandemic-related mental stress, fears and worries as well as a decline in the quality of life among children and adolescents and their families. Children and adolescents from socioeconomically 4 FOCUS number and the survey periods of the data (primary and routine data) forming the basis for the included publications were correlated to key figures of the pandemic.
In the past year, a rapid review relating to the mental health of the adult population during the COVID-19 pandemic from the Unit of Mental Health at the Robert Koch-Institute had already been presented as part of the emerging mental health surveillance [16]. So as to report most uniformly and comparably across the entire age spectrum, this rapid review refers to the rapid review on

Methodology
The methodology of this review is based on the standardised approach for the rapid review process proposed by the German Public Health Research Network on COVID-19 (https://www.public-health-covid19.de/en/) in the context of the current pandemic [11] with reference to Tricco et al.
[16]. This will be described in detail below.

Literature search
The literature search was performed on the basis of the PECO criteria using the following specifications: Population: Children and adolescents in Germany; Exposition: COVID-19 pandemic; Comparison: before/after or after COVID outbreak in Germany; Outcome: Mental health. The inclusion and exclusion criteria were: The present rapid review has thus four main goals: First, to synthesise the evidence of the quantitative research relating to the mental health of children and adolescents in Germany as well as of the data of their care with regard to mental health problems and disorders during the pandemic. The regional scope of the data acquisitions was thus limited to Germany. Studies from other countries as well as studies using mixed samples with participants from several countries were excluded. German (sub-)samples, however, were considered when the results were reported separately. For not to exclude relevant publications with participants that had reached the age of majority in individual cases, studies with participants up to an upper age limit of 20 were included in the review. When studies including a broad age spectrum up to adulthood reported results for youths up to the age of 17 separately, these were likewise included. Secondly, it is to be determined how reliably and how comprehensively the mental health of children and adolescents is represented in the included publications. To do so, the indicators, tools, and inventories used in the studies were each assigned to psychological constructs and summarised in tables. Thirdly, the databases of the included studies are assessed with respect to representativeness for the general population. In order to do so, the data representing the basis for the included publications were systematised with regard to their suitability for representative statements for the respective reference population and were depicted in tables, too. Fourthly, it will be analysed, how (well) the development of the mental health of children during the pandemic is represented in German research and the German data landscape. Thus, the PubMed and Embase databases as well as the additionally searched preprint servers ArRvix, BioRvix, ChemRvix, MedRvix, Preprints.org, ResearchSquare, and SSRN, are entered into this database on a weekly basis.
The literature database was searched for texts on mental health, school, and school closures as well as on domestic violence using several search strings (Annex Table 1) defined by filter terms. All texts extracted in this way were initially filtered by 'children and adolescents' using a fourth search string, and by their reference to 'Germany' using a fifth search string.
Manual search Beyond the systematic search in the mentioned international databases, publications were searched in additional dissemination formats, such as reports, websites of studies, press releases, or reports from health insurance funds, as it can be assumed in view of the high need for information and the resulting rapid succession of scientific publications on COVID-19 that not all findings were already listed in there. In particular, health insurance fund data is also not necessarily published in a scientific journal. The literature search was thus extended to include the following areas: (1) Systematic search in the World Health Organization (WHO) database 'COVID-19. Global literature on coronavirus disease' (last update 06.12.2021; search string see Annex Table 1). (2) Websites of COVID-19 related studies in the general population, listed on the website of the German Data Forum (RatSWD) (As at 24.11.2021). (3) Press releases and current reports or studies, respectively, e.g. from service carriers and providers of the Inclusion criteria (1) Target population: General population in Germany (as well as subgroups according to region and age) (2) Age group: Children and adolescents up to the age of 20 (3) Observational period: During the COVID-19 pandemic (4) Constructs reported: Mental health as main outcome (5) Publication of a temporal comparison (compared to measurement points before the start of the pandemic or during the pandemic) (6) Publication language: German/English Exclusion criteria (1) Publication type: Reviews, review articles, statements, comments, letters to the editor (2) Methodology: Purely qualitative data (3) Presentation of the study methodology: Methodology not presented with sufficient transparency (4) Evaluation design: Exclusively correlation analyses without reporting of frequencies or their changes in the general population, respectively (5) Target population: Subgroups beyond the above-mentioned sociodemographic characteristics (e.g. individuals with pre-existing specific mental disorders, excluding attention deficit/hyperactivity disorders (ADHS) and eating disorders)

Systematic search
The search was based on the literature database created from the library of the Robert Koch Institute in the course of the COVID-19 pandemic (As at 19.11.2021). Since the beginning of the pandemic, all publications identified by means of several search strings (Annex Table 1) in the 6 FOCUS made initially, were discussed in the team with at least three individuals and were included or excluded in an iterative process according to the above-mentioned criteria.

Systematic extraction of the relevant data
The relevant data of the included publications was extracted systematically according to the above-presented criteria and was prepared in tabular form (Annex Table 3), the used indicators were identified, classified, and likewise prepared in tabular form (Annex Table 4). This was approached on the basis of the procedure Mauz et al. [15]. The data extraction was quality-assured in each case by at least two additional individuals.

Classification of the included publications with regard to content
Primary data acquisitions with direct information relating to possible changes in the mental health of the child and adolescent population in Germany during the COVID-19 pandemic were combined under the category I 'Primary data on the mental health of children and adolescents in Germany in the context of the pandemic' (see Annex  Tables 3 and Annex Tables 4). Aspects of the care of children and adolescents in the context of mental health problems and disorders from published billing data from the National Association of Statutory Health Insurance Physicians, statutory health insurance funds, and the Federal Office of Statistics as well as from primary data acquisitions with care reference were combined under the category II 'Routine data and care-related primary data'.

Title and abstract screening, full text analysis
After the systematic search, the publications extracted thereby were subjected to a title and abstract screening. Twenty percent of the extracted publications were additionally checked by two experienced individuals (RS and AKB). This did not result in any diverging assessments. In a next step, the remaining publications were subjected to a full text analysis and were classified according to their suitability for the inclusion in the review. The publications that were found during this manual search were handled analogously. All publications were checked by at least two individuals. Publications, for which an unambiguous decision could not be 7 FOCUS

Systematisation according to the type of the data basis (study types)
Insofar as the data bases of the included publications were primary data acquisitions, a systematisation according to the acquisition design of the respective databases into the study types A-G was made based on the classification of Mauz et al. [15], but with subject-related adaptations and extensions (Annex Table 2).
Publications were assigned to the study type A, when its data basis allowed comparisons with prevalence or traits either from the pre-pandemic time period or at different points in time during the pandemic on the basis of a repetitive comprehensive survey or a repetitive cross-sectional sample drawn by means of a random process, or a population-representative quota sampling.
Publications, the data basis of which represented a representative trend study, based on a repetitive sample drawn by means of a random process or by means of a population-representative quota process from an access panel, were assigned to study type B.
Publications, the data basis of which was based on a one-time comprehensive survey or cross-sectional study, based on a sample drawn by means of a random process from a reference population, an access panel, or a population-representative quota sampling, were assigned to study type C, in turn.
Lastly, publications, the data basis of which was a longitudinal study with a representative initial sample at the first survey point, which allows drawing conclusions to population-based intra-individual changes, were assigned to study type D. According to the procedure of Mauz et al.

Classification of the indicators mental health
The indicators, tools, and inventories relating to the survey on the mental health of children and adolescents, which were reported in the included publications, were classified, analogously to the approach in Mauz et al.
[15], but adapted to child and adolescent age, initially according to their higher-level outcome areas as follows (see also Annex Table 4 Another contextual breakdown according to the respective identified constructs as well as the used inventories and survey tools (outcome type a-d) or the respective identified care areas (outcome type e and f), was made within the classification of the outcome types. On the one hand, these assignments are to make it possible to assess, how comprehensively the mental health among children and adolescents in Germany during the COVID-19 pandemic was captured, and, on the other hand (with regard to the use of standardised and validated tools), the reliableness, with which the contextual outcome areas were surveyed.

Course of the pandemic and temporal correspondence of the data acquisitions
To analyse to what extent the data acquisitions, on which the included publications are based, reflect the course of the pandemic since March 2020, and for which phases of the pandemic they allow conclusions to be drawn, the observational periods of the respective data acquisitions for all included publications were determined and were compared with the development of the incidences and death rates during the COVID-19 pandemic ( Figure 2). Based on the continuously updated division of the pandemic phases according to Schilling et al. [20,21] and Tolksdorf et al. [22], the course of the pandemic until the end of the inclusion period of the review on 19.11.2021 was divided in retrospect into six phases: 1. Wave 1 from mid-March to mid-May, 2. Summer plateau 2020 from mid-May to the end of September 2020, 3. Wave 2 from the beginning of October 2020 to the end of February 2021, 4. Wave 3 from the beginning of March to mid-June 2021, 5. Summer plateau 2021 from mid-June to mid-July 2021, as well as 6. Wave 4 starting in August 2021.
As with Mauz et al. [15], the observational periods of the data acquisitions, on which the included publications are based, were specified in intervals of half months over the total period of the pandemic. Periods, for which the data for at least seven days were available in the respective half of the month, are presented. If this did not apply for any study types A-D were classified as being methodologically more reliable with regard to their informative value for the general population. In contrast, cross-sectional studies with non-representative, self-selected samples (i.e., convenience samples; study type E) were classified as being methodologically reliable only to a limited extent with regard to their population-representative statements, as well as repeated crosssectional surveys (study type F) or longitudinal studies (study type G) on the basis of non-representative initial samples.
Routine data was assigned to the data sources, which were deemed methodologically more reliable with regard to their statements about the general population, with the informative value being comparable with study type A-D. They result as part of documentation and billing processes of statutory health insurance funds or in official statistics, representing comprehensive surveys of the respective population, and are thus representative for it. In the case of statutory health insurance funds, they are representative, for instance, for the respective insured clientele. In the case of publications from the data of individual health insurance funds, a weighting (e.g. by age and sex) is also often made using the German microcensus data in order to obtain an adaptation to the general population [see 17]. Publications with results from care-related primary data acquisitions were systematised in the same way as the primary data acquisition of category I. Even if they do not provide any primary data in the strict sense, data from networks of medical practices [18,19] were also included in the carerelated primary data acquisition in this review becausecontrary to, for example, the routine data from statutory health insurance funds -they represent a selective and not a comprehensive survey of the respective population. 9 FOCUS population (study type A), nine publications from three trend studies with random sample from an access panel (study type B), and one publication each from five representative cross-sectional studies (study type C) with six data bodies (one study reported from two different data bodies, medical clinic and school sample [23]) were included in the review. Three studies with one publication each originated from population-based longitudinal studies (study type D). Five cross-sectional studies with one publication each (study type E), a repetitive cross-sectional study with one publication (study type F), and three longitudinal studies with one publication each (study type G) were based on non-representative non-probability samples. A total of 19 publications from 13 data bodies are thus available with regard to category I as data bodies (study types A, B, C, and D), which are assessed as being comparatively reliable with respect to their informative value about the general population. Nine publications from nine data bodies belonged to the study types E, F, and G, which are rather more susceptible to bias with regard to their suitability for representative statements for the general population.
From the routine data, five publications from four data sources are available in category II 'Routine data and care-related primary data'. A total of four publications from three representative cross-sectional studies (study type C) and three repetitive cross-sectional studies with non-probability samples with one publication each (study type F) were included in the case of the care-related primary data. Four publications from three studies, which are assessed to be reliable with respect to their informative value about the general population, half of the month, the study was assigned to the period with the most study days.

Literature search
At the end of the multi-stage inclusion and exclusion process according to the above-mentioned criteria, 983 publications relating to Germany were extracted according to these criteria from the systematic search (as of: 19.11.2021), 24 of which were suitable for the inclusion in the review after manual exclusion. A total of 478 publications (As at 10.02.2022) were found using the manual search. Fifteen of them were suitable for an inclusion in the review. A total of 39 publications could thus be included in the review ( Figure 1).

Classification of the included publications according to context and systematisation according to study types
A total of 28 publications from 22 primary data acquisitions (category I 'Primary data on the mental health of children and adolescents in Germany in the context of the pandemic'), five publications based on four routine data sources, and seven publications from six care-related primary data acquisitions (category II 'Routine data and care-related primary data') could be included in the review. With regard to category I 'Primary data on the mental health of children and adolescents in Germany in the context of the pandemic', a total of two publications from two trend studies with random samples from the general

Result synthesis according to indicator type and data basis
(a) Indicators of positive mental health A total of 16 of the 39 publications included in the review contained indicators of the positive mental health from a total of twelve data bodies. These could be assigned to three higher-level constructs: quality of life/wellbeing, life satisfaction, and general health (Annex Tables 3 and Annex  Tables 4). Results from publications of the study types A-D as well as E and G are available for indicators of positive were available with regard to the care-related data. Three publications from three data bodies are considered here to be the study types, which are rather more susceptible to bias in this respect.
In consideration of all included publications, more than two thirds (28 of 39) of the publications or two thirds of the underlying data sources (20 von 32), respectively, can thus be assigned to the study types A, B, C, and und D, which are assessed to be rather reliable with regard to their informative value about the general population, or to the routine data, respectively. With regard to the quality of life, a paper of the study type E did not find any changes between a pre-and post-lockdown group with children and adolescents under the age of 12 [36] for the first wave of the pandemic. In contrast, a study of the type G that collected data from April to the beginning of May 2020 found an intra-individual decline of the quality of life and a deterioration with regard to the emotions, mood, and the overall satisfaction among children between the ages of 3 and 10 during the first lockdown with small to average effect sizes. However, it found also improvements in leisure time activities and family life [37]. mental health. In the respective studies, mainly standardised and validated survey tools were used, but also single items.
A significant increase of the proportion of children and adolescents with reduced health-related quality of life compared to the pre-pandemic period was reported from analyses of the study types A and B from the COPSY study for the period of the first wave of the pandemic, both at the federal level [24-26] and for the city and federal state of Hamburg [27]. Children, who belonged to a risk group, formed from being part of families with low education, migration background, or cramped living conditions, were significantly more affected [24][25][26][27]. Compared to the pre-pandemic period, the general state of health had not changed [27]. However, declines in the subjectively assessed general activity among 14-to 17-year-olds was reported from the pairfam study (study type B) [28]. Results from the second survey wave of the COPSY study from December 2020 until January 2021, conducted in parallel to the second wave of the pandemic, showed a further decline of the health-related quality of life compared to the first COPSY wave, but with negligible effect sizes [29]. Results from the study 'Präventionsradar' (Prevention Radar) of the Institute for Therapy and Health Research (IFT-Nord; Study type C), a long-term study in 13 states with more than 14,000 children and adolescents from 897 classes, showed a decline of life satisfaction among pupils in grades 5 to 10, on average by approximately 21% [30] in the initial phase of the pandemic. Declines of life satisfaction compared to the pre-pandemic period were also reported from the BerO study (study type B) in the spring of 2020 for high school graduates [31] as well as further declines in the course of increases in perceived stress up to a proportion of four fifth of the children and adolescents between the ages of 7 and 17 was reported from studies of the study type B (COPSY study) [39]. An increase in the perception of stress by approximately one third to above 50% was reported by high school graduates in a survey conducted in six federal states (BerO study) [32].
Experiencing a large amount of stress was also reported from papers of the study type C. At the time of the first lockdown (May 2020), 42% of the parents of 10-to 17-yearold children and adolescents indicated in a nationwide representative survey that the Corona crisis stressed their child strongly or very strongly, respectively [34]. In a retrospective survey by the German Network of Academic Medical Research (NUM), conducted from November 2020 to April 2021 in parallel to the second wave of the pandemic, the proportion of children and adolescents between the ages of 11 and 17, who−according to self-reporting−were mentally stressed, was approximately two thirds in a population-based (pre-)school sample. According to information from parents, in contrast, approximately four fifths of the participants felt stressed [23]. In the same sample, decreases of stress among children and adolescents before and during the pandemic were reported in the amount of 11% (self-report) and 4% (parents'-report), respectively. Similar results were specified for a clinical sample from paediatric mental health clinics which was analysed comparatively in the same publication [23]. According to a nationwide representative study of the type C on behalf of the statutory health insurance fund DAK-Gesundheit, almost two thirds of the children and adolescents between the ages of 10 and 17 worried about the impacts of the (b) Indicators of mental distress Indicators of mental distress were identified in a total of 19 of the publications included in the review on the basis of 15 data bodies. They could be assigned to four constructs: 1. Perceiving stress (such as COVID-19-associated mental stress, sadness or affects), 2. Perceived stress, 3. Loneliness, and 4. (COVID-19-associated) worries (Annex Table 4). In the respective studies, mostly non-validated survey tools in the form of single items were used for the assessment of the indicators of mental stress, oftentimes without citing a specific reference. The use of standardised and validated tools was reported in only five publications.
Regarding the study types A and B, by more than two thirds of the children and adolescents between the ages of 7 and 17 from the COPSY study was reported that they felt stressed by the COVID-19 pandemic, both for the city and federal state of Hamburg (study type A) and nationwide (study type B) in the initial phase of the pandemic (from May to July 2020) [24-27]. For 7-to 17-year-old children and adolescents from families with low education, migration background and/or with cramped living conditions (<20m 2 living space/person), a higher stress was reported from May to June 2020 [24,26]. However, for the period between May and July 2020−the time of the summer plateau 2020−a decline in perceived stress compared to the pre-pandemic period (October 2018 to August 2019) was described from the pairfam study (study type B) for 14-to 17-year-old adolescents [28]. With regard to feelings of loneliness among adolescents between the ages of 13 and 17, an increase compared to the pre-pandemic period was reported from the pairfam study [28,38]. During the second wave of the pandemic from November 2020 to January 2021, further Across all outcomes and indicators a significant increase of mental distress and symptoms can be observed during the pandemic.
14 FOCUS beginning of May 2020, mental stress was found among half of the participating 3-to 10-year-old children [37]. In contrast, the study 'Kind sein in Zeiten von Corona' ('Being a child in times of Corona', study type E), performed between mid-/end of April and mid-/end of May 2020, reported that the majority of the children between the ages of 3 and 15 handled the Corona crisis rather well or well [42]. Particularly in families with high parental educational status, more parents reported that their children handled the pandemic well, compared to families with low education of the parents [42]. Almost one third of the surveyed parents of children and adolescents between the ages of 3 and 15 also reported that their child felt lonely during the pandemic [42]. For children from families with difficult financial situation, loneliness was reported more frequently than for children from families with good financial situation [42]. According to a further analysis of the study type E, conducted in the period between April and June 2020 among children and adolescents between the ages of 5 and 19 with and without mental health problems, a proportion of approximately two thirds felt socially isolated due to the pandemic [43]. In an additional survey as part of the school entry health examinations in the region of Hanover (study type F), an increase of fears as well as an increase in the prevalence of sadness and fits of rage (retrospectively) compared to the pre-pandemic period was reported among school starters from September 2020 to February 2021 − approximately the period of the second wave of the pandemic [44]. With only a few percentage points, however, the increase was comparatively small [44]. In the LIFE Child Study, a longitudinal study of the study type G with non-representative non-random sampling of the initial sample and COVID-19 pandemic, with regard to their own Coronavirus infection, or the infection of someone close to them, during the first wave of the pandemic [34]. Between 2020 and 2021, in the prevention radar of the IFT-Nord (study type C) almost half of the surveyed 14,287 pupils in grades 5 to 10 from a total of 897 classes in 13 federal states reported that they felt stressed often to very often [30]. On the basis of a validated inventory, from a nationwide longitudinal study with a representative initial sample, conducted by the University Medical Centre Hamburg-Eppendorf in cooperation with the German Centre for Addiction Research in Childhood and Adolescence (study type D), an intra-individual increase in the perception of stress among children and adolescents between the ages of 10 and 17 was reported during the first wave of the pandemic until April 2020 compared to the pre-pandemic period (September 2019) [40].
Results relating to the perception of stress as well as relating to social isolation and loneliness were reported from type E studies. Compared to the pre-pandemic period in a study by the Department of Paediatric Psychiatry at the University of Dresden including former patients as well as their families, increases in mental stress in the form of worries, fears, and emotions among children and adolescents with and without mental problems between the ages of 1 and 17 were reported at the beginning of the pandemic (beginning of April to beginning of May 2020). Among children and adolescents without mental problems, reported increases were even stronger [41]. According to a crosssectional study of the Ludwig-Maximilians-Universität München with non-random convenience sampling (study type E) with data acquisition from the end of April to the 1. Psychopathological symptoms in general 2. Psychosomatic problems 3. Eating disorders 4. Depressive symptoms 5. Symptoms of an anxiety disorder.
In these studies, standardised and validated survey tools or inventories, respectively, were used. Only one study [44] did not. In one publication [47], modified items of various subscales of a validated inventory (Strengths and Difficulties Questionnaire; SDQ) were combined to form a new, non-validated total score ('problem behaviour'). In another publication, the subscale of a validated inventory (State-Trait Depression Scales; STDS) was recoded and was provided with a reverse meaning (from 'positive mood' to 'anhedonia', i.e. no longer being able to experience joy) [38].
Compared to the pre-pandemic period, partially significant increases in the prevalence of general psychopathological symptoms [24-27, 44] as well as of depressive symptoms [24-29, 38, 48] and of anxiety disorder symptoms [24][25][26][27] were reported for the initial phase of the pandemic from the studies of type A and B. Almost a doubling of the prevalence of mental health problems (SDQ) for 7-to 17-year-olds from a total of 17.6% in the pre-pandemic period to 30.4% in May/June 2020 was reported nationwide from the first wave of the COPSY study [24][25][26]. However, no prevalence changes were reported for the city of Hamburg (COPSY Hamburg study) [27]. However, the survey period was later here, from mid-June to mid-July 2020, and was already characterized by a first decline of the COVID-19 incidences ( Figure 2) and -associated therewith -relative easing of the strict containment measures three survey times conducted in the region of Leipzig, the proportion of children between the ages of 9 and 19, who had no contact with their friends, rose from 3% to 13% (T1) or 14% (T2), respectively (T0: before the pandemic, T1: last week in March 2020, T2: last week in April 2020). The region, however, was affected only little by COVID-19 infections at that time [45]. In that study, approximately 80% of the children missed also personal contacts with their friends [45]. With regard to fears and worries relating to COVID-19, most of the children worried more about the health of their families than of their own. Sixty percent worried at least moderately about the international situation, 20% were afraid of COVID-19 themselves [45]. It was furthermore reported that the proportion of children who believed that the situation would never be the same again after the pandemic, more than doubled within one month (from T1 to T2), from approximately 7% to approximately 16% [45]. In a diary study on the mental effects of homeschooling (study type G) performed with parents of 6-to 19-year-olds from March 27 to April 3, 2020, less positive affect and more negative affect of their children was reported on days when schoolwork had to be done or when the parents were concerned directly with the learning, than on days when this was not the case [46].
(c) Indicators of acute symptoms of a mental disorder In a total of 16 of the included publications, stemming from 11 data bodies, tools and inventories for the screening of general psychopathological symptoms as well as those focussing on specific mental health problems and disorders were used. These could be assigned to five contextual constructs: ble effect sizes [39]. With regard to depressive symptoms, information is available from the papers of the study types A and B from seven publications [24-28, 38, 48] on the basis of two data bodies (COPSY study and pairfam study). From the pairfam study with an additional COVID-19 survey among 14-to 17-year-old children and adolescents for the period between mid-May 2020 and mid-June 2020, mean value changes for anhedonia and negative mood were reported, which indicate increases in depressive symptoms (compared to mid-October 2018 to mid-August 2019) [38]. With regard to the prevalence of clinically relevant depressive symptoms, increases by 150% (from approximately 10% to approximately 25%) were reported for the same period [28, 48], with significantly higher increases among girls than among boys [48]. In contrast, no increases of depressive symptoms could be determined in the COPSY study from the pre-pandemic period until wave 1, but there was a slight increase (from 11.3% to 15.1%) from the first survey wave from the end of May to mid-June 2020 to the second wave from mid-December 2020 to mid-January of 2021, but with negligible effect sizes. As to the symptoms of a generalised anxiety disorder, however, partially significant increases were reported on the basis of various measuring tools, both nationwide (14.9% to 24.1%) [26] and for the city and federal state of Hamburg (from 15% to 26%) [27]. A further prevalence increase to 30.6% was measured nationwide in the second survey wave of the COPSY study from mid-December 2020 to the end of January 2021 [39].
Studies assigned to the study type C with retrospective surveys partially arrive at the same, partially at different results with regard to general mental health problems as the studies of type A and B. While no increase of mental after the first wave of the pandemic. For a risk group of children and adolescents from families with low education, migration background and/or with cramped living conditions (<20m 2 living space/person), more mental health problems were reported in COPSY wave 1 than for children and adolescents, who do not belong to this group. Members of the risk group reported more emotional and conduct problems, hyperactivity and more peer relationship problems, in each case with medium to high effect sizes [26]. In the second survey wave of the COPSY study (study type B) from mid-December 2020 to the end of January 2021, parallel to the second wave of the pandemic (see Figure 2). At 30.6%, the nationwide prevalence of mental health problems remained high [25]. The routine parent survey as part of the school entry health examinations in the region of Hannover (study type A), showed a continuous increase in mental health problems among school starters of the school starter cohorts 2017/2018 to 2020/2021, but at a much lower level (from 5.5% in 2017/2018 to 8.0% in 2020/2021) [44]. For the study types A and B, reports about increases of psychosomatic problems during the first wave of the pandemic, in particular with regard to irritability, bad mood, headaches and abdominal pain, are available from the COPSY study both for the nationwide sample and for the Hamburg sample [24,27]. Here, children and adolescents from a risk group (i.e., families with low education, migration background and/or cramped living conditions (<20m 2 living space/person)) were again reported with more psychosomatic problems [24,26]. In December 2020/January 2021, during the second wave of the pandemic, additional slight increases of psychosomatic problems were reported, but with negligi-17 FOCUS non-representative sampling basis found intra-individual declines of 'problem behaviour' during the first lockdown (data acquisition from the end of April to the end of May 2020) as well as additional declines during the time of the first easing (mid-July 2020) [47].
(d) Indicators relating to the experience of violence in the context of the pandemic Indicators relating to the experience of violence by children and adolescents in the context of the pandemic could only be found in one of the total of 39 publications included in the review from one data body. The two indicators identified in this study were both assigned to the construct 'experience of violence'. A single item as well as a list experiment was used for the survey. In the case of a list experiment, participants of a study are randomly assigned to one of two lists. One list (reference group) includes four general questions, the second list (treatment group) includes the same four questions, plus a sensitive item. The participants have to specify in each case, how many of the items apply to them (e.g. three of five). A conclusion can be drawn from the comparison of the average total number between reference and treatment group to the prevalence of the subject matter surveyed with the sensitive item, which is less readily accessible to the direct survey (e.g. experiencing sexual or severe physical violence).
In the study of the type C, performed from April to May 2020 by the Technical University of Munich and the Leibniz Institute for Economic Research in Essen, a prevalence of approximately 6.6% was reported for physical punishment among children and adolescents during the first phase of the pandemic, for children of women with a health problems and only small associations between COVID-19-related stress and mental health problems were reported from an analysis by the Network of Academic Medical Research (NUM) with a (pre-)school sample of 4-to 19-year-old children and adolescents [23], a birth cohort study from Ulm among 6-to 7-year-olds found strong mean value increases, which were interpreted as increase of mental health problems, only among girls [33]. In the study 'Prevalence Radar' of the IFT-Nord, in which the emotional problems scale of the SDQ was deployed, increases of emotional problems from a total of 9.2% during the 2018/2019 school year to 13.9% during the 2020/2021 school year were reported descriptively [30]. The increase was stronger among girls, from 14.9% to 22.9%, which corresponds to a relative increase by 53%. Among boys, the frequency increased from 3.8% to 5.5%, thus by 45% [30]. A publication of the study type D between mid-May and the end of July 2020 reported descriptive mean value increases among children between the ages of 5 and 7 for emotional problems, hyperactivity, and conduct problems [49].
Compared to a pre-and post-lockdown group, a study of the study type E with children and adolescents under the age of 12 did not find any differences with regard to mental health problems, eating disorder symptoms, and depressive symptoms as part of a cross-sectional survey. However, a decline with regard to the subscale conduct problems of the SDQ as well as a decline of the number of planned suicides was reported in the survey period from mid-March 2020 to the end of August 2020 (compared to a period from the end of November 2018 to mid-March 2020) [36]. A longitudinal study of the study type G on a 18 FOCUS exceeds the number of inpatient treatment cases. Utilisation data for groups of medical specialists who are primarily tasked with caring for children and adolescents with mental health problems and disorders, is reported below: paediatricians as well as paediatric psychotherapists [vgl. 53].
In April and May 2020, in the early phase of the pandemic, compared to the corresponding months of 2019 or 2018/2019, respectively, billing data for the outpatient and inpatient area show significantly declines in the paediatric, child and adolescent psychiatric as well as a child and adolescent psychotherapeutic treatment cases by up to one third [17,51]. Catch-up effects in similar magnitudes are reflected in June 2020 with increases compared to the corresponding period. Parallel to the second wave of the pandemic, a decline of the case numbers occurred again in the last quarter of 2020. With regard to utilising paediatric services, there were strong declines again for the first half of 2021 for January, February, April, and May, whereas there were strong increases of the treatment cases for March and June 2021, compared to the pre-pandemic period. This is likewise reported for the number of the paediatric psychiatric treatment cases as well as for the paediatric therapeutic treatment cases, while the level of the latter fluctuated in the remaining months around the respective corresponding pre-pandemic period [17,51]. Based on the paediatric utilisation, the decline at the preschool and primary school age (up to the age of 9) was lower than among older children and adolescents (between the ages of 10 and 17), here compared to the numbers for 2020 with pooled utilisation data from 2018/2019 [17]. However, a reversed usage pattern was reported for the utilisation of psychiatrists or psychologists, respectively: Here, the reported high-risk profile of almost one fourth (23.3%). If children under the age of 10 lived in the household, the risk for physical punishment increased fivefold [50]. High depression and anxiety values of the respondents and/or of the respective partners increased the risk for physical punishment of the child. A prevalence of approximately 2% was reported for severe physical violence against children during the pandemic [50].
(e) Indicators from routine data Indicators from routine data were reported in five publications from three data sources. They were assigned to three care areas: 1. Outpatient care (two publications from one data source), 2. Inpatient care (one publication from one data source), as well as 3. Child protection (two publications from two data sources). Key figures, such as the number of treatment cases, utilising outpatient medical care due to mental or behavioural disorders, the number of acute or latent cases of child endangerment, as well as the number of the child protection cases reported by schools or day-care centres, were evaluated.
The results from the routine data on the outpatient care of individuals with statutory health insurance utilising care provided by SHI-accredited physicians, are based on the data from 16 of the total of 17 Associations of Statutory Health Insurance Physicians (without Mecklenburg-Western Pomerania) and are provided by the Central Research Institute of Ambulatory Health Care in Germany (Zi) [51,52]. In the DAK 'Kinder und Jugendreport 2021', outpatient and inpatient health care utilisation is presented jointly [17]. They are reported in the outpatient care section here because the number of outpatient treatment cases 19 FOCUS of the eating disorder cases treated on an inpatient basis was 9% above the previous year [17]. In the case of depression and anxiety disorders (reported in combination), in contrast, a decline of the hospitalisation rate was determined for the 10-to 17-year-olds during the first lockdown of 2020 (-37%) and a rather slight increase after the first and during the second lockdown compared to the previous year [17]. Based on all of 2020, the hospitalisation rate for depression and anxiety disorders compared to 2019 remains unchanged [17].
The child protection cases reported to child protective services by kindergartens during the first lockdown in April 2020 decreased by one third, the child protection cases reported by schools by more than half [54]. The acute and latent cases of child endangerment reported by child protective services to the Federal Office of Statistics increased significantly from 2019 to 2020. In comparison, the increase was 9% [55]. However, there were already increases by 10% each in 2018 und 2019, so that this development appears to follow a more general trend.
(f) Indicators from care-related primary data acquisitions Results relating to indicators from primary data acquisitions relating to care are taken from seven publications from six data bodies. They can be assigned to three care areas: 1. Outpatient care (two publications from two data bodies), 2. Inpatient care (one publication from one study), and 3. Child protection (four publications from three studies). Publications from the study types B, C, and F are available with regard to the care-related primary data.
For the area of outpatient care, a decline of the utilisation of paediatric care is consistently reported from the usage declined during the first lockdown among the children of primary school age, while it increased among older children and adolescents. After the first lockdown and during the second lockdown, increases of the utilisation rates were recorded here among all age groups [17].
Based explicitly on diagnostic data for mental and behavioural disorders (ICD-10: F00-F99), a decline of outpatient doctor's visits by a total of 11% of statutorily insured children between the ages of 0 and 12 between the second quarter of 2019 and the second quarter of 2020 was determined in an analysis on the basis of the nationwide billing data from the National Association of Statutory Health Insurance Physicians. The decline was smaller for preschoolers than for school-age children [52]. Likewise based on the ICD-10 diagnostic group F00-F99, no differences between 2018, 2019, and 2020 were reported in the DAK Kinder-und Jugendreport 2021 for an age group between 0 and 17 years. Based on the prevalence and incidence of the 10 most frequent disorders, the number of the combined outpatient and inpatient treatment cases in 2020 did not differ from those of the previous year, with respect to the year as a whole [17].
With regard to the inpatient care, an increase of the hospitalisation rate for eating disorders (bulimia and anorexia) among the 5-to 17-year-old children and adolescents by 16.3% compared to the period of the previous year was reported from the data of the statutory health insurance fund DAK-Gesundheit during the first lockdown of 2020 (11.-17. calendar week). While there was still an increase by 3.2% after the first lockdown (18.-44. calendar week), this increase was 26.1% during the second lockdown (45.-52. calendar week). Based on all of 2020, the number 20 FOCUS child protection services in Germany (n=575; response rate 65%) of the study type C, one fifth of child protection services reported declines with regard to risk reports, and one fourth reported declines with regard to individuals taken into care for the period between the first lockdown in 2020 [58,59]. For the spring of 2021 (compared to the spring of 2020), an increase in performed home visits from longterm outreach care was reported in a survey by the national centre for early intervention of 82 healthcare professionals (study type F), by 60% of the respondents (family midwives and family, health, and paediatric nurses). One fourth of the professionals did not report a change, 17% reported a decline of the home visits [60]. Figure 2 shows the course of the pandemic based on the incidence and death numbers due to SARS-CoV-2 since the beginning of the pandemic in March 2020 to the end of the inclusion of published data and publications from the systematic search in this review on 19.11.2021. The observational periods of the data acquisitions, on which the publications included in this review are based, are entered below. The observational periods of most of the data bodies included in this review were between March and May 2020, with a peak in the second half of April and the first half of May 2020 -and thus in the period of the first wave of the pandemic with its comparatively low number of infections and deaths. A second, but significantly smaller accumulation of the number of observational periods can be found in the second wave of the pandemic with its For the inpatient area, the PSYCHIATRY Barometer (study type C) reported a significant decline of the occupancy rate of the fully and semi-inpatient paediatric mental health facilities by almost 30% for 2020 compared to the pre-pandemic period in a comprehensive survey of all psychiatric and psychosomatic specialist hospitals as well the general hospitals with psychiatric or psychosomatic specialist departments (participation: n=312) [56]. The vast majority (90%) of the paediatric mental health facilities indicated that a decision against an inpatient treatment was rarely or never made due to the COVID-19 pandemic. Of approximately one third of the surveyed facilities, wards were temporarily closed or combined due to the COVID-19 pandemic.

Course of the pandemic and temporal correspondence of the data acquisitions
From a survey of all paediatric clinics (participation: 159 out of 365) in Germany in March and April 2020 relating to child protection, a study of the C type reports a decline of child protection cases by 37% compared to the pre-pandemic period. In the inpatient area, the decline was even stronger than in the outpatient area [57]. In a survey of all 21 FOCUS differentiated in data bodies, which were deemed reliable with regard to their informative value for the general population (study types A-D) or into data bodies, which are only reliable to a limited extent (study types E-G). The state of research developed for this review will be combined below, the results will be classified with regard to the reliableness and representativeness of their database, the operationalisation and validity of the outcomes, as well as the respective observational period and− compared to the results from the adult review, where possible, and conclusions will be drawn.
Number of studies and ratio of the study types In spite of a longer inclusion period (the inclusion period of the adult review ended on 31.07.2021 [15]) and in spite of expanded inclusion criteria (school-related publications relating to mental health as well as publications relating to child protection were additionally considered in the child review), a smaller number of publications was found for the childhood and adolescence than for adulthood, even though the inclusion of publications was handled comparatively generous (e.g. studies with participants up to the age of 20 were considered, as well as studies, which did not focus primarily on the changes in the mental health of children during the pandemic, but which provided pre-and post-pandemic results, for example, in the sample description). It is unclear if that reflects a lower (research) interest in the mental health of the child and adolescent population during the pandemic or if this is due to practical research aspects, such as higher ethical and data privacy requirements in studies with minors. However, the ratio between publications with a database that is deemed reliable with significantly higher infection and death rates starting in October 2020 until the end of February 2021. The third wave of the pandemic March 2021 to June 2021 is hardly reflected in the number of ongoing data acquisitions on the basis of the publications included in this review. No information relating to data acquisitions was available for the fourth wave of the pandemic, starting in mid-August of 2021 until the end of the inclusion period of published study results on 19.11.2021.

Discussion
It was the goal of this rapid review to combine the available evidence relating to the changes of the mental health of children and adolescents in Germany during the COVID-19 pandemic, to classify the available data sources by their informative value for the general population, to assess the scope and the reliability of the representation of mental health aspects in the included studies and data sources, as well as to analyse how the mental health of children and adolescents is represented in the German research and data landscape in the course of the pandemic. To do so, a total of 39 systematically and manually searched publications from primary data acquisitions among children and adolescents themselves or from their parents as well as from routine data and from care-related primary data acquisitions were included for the period from the beginning of the pandemic mid-March 2020 until 19.11.2021. According to the procedure of the preceding rapid review on the mental health of the adult population in Germany during the COVID-19 pandemic [15], the databases of the included publications were systematised and 22 FOCUS included in this review, possibly to keep the survey economical. Therefore, based on the included publications, no statement about a possible increase of mental disorders can thus be made. Indicators relating to the experience of violence were reported most rarely (only a single study was found on this topic, which met the inclusion criteria).
Development of the mental health of children and adolescents during the pandemic In contrast to the results of the adult review [15], a significant impact of the pandemic on the mental health of children and adolescents in Germany was evident from the results of the studies of the types A-D, which were classified as being reliable with regard to their informative value for the general population and with regard to the survey methodology -both in the overall analysis across all outcome areas and across all indicators. Significant increases of the proportion of youths with limited quality of life, declines in the life satisfaction and the general subjective health, increases of different forms of perceptions of stress, and increases of general psychopathological symptoms as well as increases of symptoms of specific mental disorders compared to the pre-pandemic period were reported from these study for the initial phase of the pandemic. This was true both for boys and for girls, as well as for different age groups. Rates between approximately 50% and 80% of children and adolescents who indicated to be mentally stressed by the pandemic were reported from various studies [24-27, 31, 32, 34, 39], based mostly non-validated on single item survey. Even though prevalence of general mental health problems, which were surveyed using standardised and validated tools, were significantly lower with regard to representativeness of the general population (study type A-D) and studies based on non-representative samples (study type E-G) was similar as for adults (approximately 2/3 to 1/3) [vgl. 15].
Spectrum and validity of used indicators A similarly broad spectrum of used indicators and tools for surveying the mental health as among the adults could be found in the primary data publications relating to the mental health of children and adolescents during the pandemic [15]. They could be assigned to the outcome areas 'positive mental health', 'perceived stress', 'symptoms of an acute mental disorder', as well as 'experience of violence'. None of the included publications reported resilience factors. Indicators relating to perceived stress were reported most frequently, indicators of acute symptoms of a mental disorder were reported second most frequently, and indicators of positive mental health were reported third most frequently. To survey mental stress in the context of the COVID-19 pandemic, mainly single items were used, often without indication of source. The validity and reliability of such information are limited. They should thus be interpreted carefully. In particular, these results were nonetheless discussed prominently in press releases [e.g. 61, 62]. In contrast, mainly standardised and validated tools were used to survey acute psychopathological symptoms as well as the positive mental health. However, using screening instruments for general or specific psychopathology only symptoms of mental disorders can be detected, they are not suitable for making diagnoses of mental disorders. To do so, more complex psycho-diagnostic interviews would be required, which were not used in any of the studies pandemic-related fears and worries, about loneliness and the feeling of social isolation among children, their desire to see their friends again, as well as negative affect due to homeschooling [41,45,46].
In spite of individual differing findings, the results from the publications of the study types A-D suggest a significant increase of mental stress among children and adolescents during the pandemic, in particular during the waves of the pandemic, which were accompanied by official non-pharmaceutical containment measures. The child and adolescent population thus turned out to be more vulnerable than the adult population [15]. The findings from the publications of the non-representative study types E-G vary more strongly but should be interpreted carefully due to incalculable potential biases. Some findings suggest that, overall, children and adolescents themselves possibly rated their pandemic-related stress as slightly less serious than did their parents because in some studies, the stress rates surveyed via self-reporting among children were below those, which were determined via the parents [23].

Vulnerable groups
In general, there were only few results from the included publications relating to specific sociodemographic groups. For children and adolescents from socioeconomically disadvantaged families, a lower quality of life, more perceived stress, more feelings of loneliness, and more psychopathological symptoms were reported than for children from socioeconomically better-off families-both from publications of the study types A and B, which are more reliable with regard to population-based statements, and from the non-representative study type E. However, the attributable approximately 30%, they had almost doubled compared to the pre-pandemic period [24][25][26]. With regard to specific psychopathological symptoms, the findings differed: While one study reported increases of depressive symptoms of 150% [28, 48], another study did not find any changes in depressive symptoms, but significant increases of anxiety disorder symptoms [26,27]. According to the results of a representative study, one in fifteen children suffered physical punishment during the pandemic and two percent severe physical violence [50]. In total, the results suggest that the mental disorders for children and adolescents varied with the course of the pandemic. For example, mostly smaller stress and mental health problems rates were reported from studies, the survey period of which was in the summer plateau of 2020 with the easing of measures [27]. Vice versa, increased perception of stress and higher mental health problems rates were reported when the survey periods corresponded temporally with the waves of the pandemic and the official containment measures associated therewith [39]. Concerning the publications of the study types E-G with non-representative sampling base, the results were less unambiguous. Some of these publications did not report any changes with regard to the quality of life, general psychopathological symptoms, depressive or eating disorder symptoms before and during the lockdown measures [36]. Partially they even reported declines, for instance with respect to planned suicides or 'problem behaviour' [36,47]. A non-representative study from the beginning of the pandemic found that children and adolescents with pandemic-related stress managed mostly well or very well [42]. Other publications of these study types, in contrast, reported a high level of Research activities and the course of the pandemic The number of ongoing data acquisitions (for each half month) was highest during the first wave of the pandemic until and including the summer plateau of 2020 with comparatively low COVID-19 incidences and pandemic-associated deaths. With each new wave of the pandemic, the number of ongoing data acquisitions corresponded less with the infection rates. For the fourth wave of the pande mic, information with regard to ongoing data acquisition relating to the mental health of children and adolescents was not available until the end of the inclusion period of the systematic search for the child review on 19.11.2021. This finding largely corresponds to that from the review on the adult population [15]. Even if making allowances for the fact that studies, even on the basis of routine data, is (can be) always published only with a certain temporal latency, it appears as though the novelty of the pandemic initially triggered a keen research interest, which declined significantly in the further course of the pandemic. This is not least supported by the fact that many ad-hoc studies were carried out at the beginning of pandemic and during the first part of the pandemic could not be determined from these study results. It can be assumed that such differences already existed before the pandemic. The results were furthermore of children with low-education parents reported in part for a combined risk group owith, with migration background, and cramped living conditions, which makes it impossible to quantify specific risks. From non-representative studies, there were indications that the pandemic could also have had relief effects for children and adolescents with pre-existing mental disorders: They were found to have fewer fears and concerns than children and adolescents without mental disorders [23,41].
On the basis of the included publications, possible differential developments in sociodemographic subgroups cannot be traced reliably. Even though there are indications about health inequities in the context of the mental health of children during the pandemic, a systematic identification of risk groups -requirement for a planning of tailored prevention and health promotion measures to target these groups -is still pending.
Health care Results from both the routine and the care-related primary data showed declines of the outpatient utilisation of specialists with subsequent catch-up effects during the first and second wave of the pandemic, whereby an increase of outpatient depression and anxiety disorder diagnoses, in particular among girls, was reported [18,51]. During the second wave of the pandemic, a similar picture emerged for the outpatient utilisation [51].
Results relating to the inpatient care indicate an increase of the treatment of eating disorders with simultaneous 25 FOCUS have contributed to the poor risk group identification, whereby no information is available from the systematic literature search and the title/abstract screening that proportionately significant sociodemographic subgroups of the children and adolescent population were overlooked.
The age limit for the study inclusion was set to be 20 so as not to eliminate relevant studies with participants, who were already of legal age in some cases. However, statements about the transition into young adulthood or young adulthood itself cannot be made therewith. The physical and mental health of children and adolescents are closely linked. Chronic physical health disorders such as obesity also have a significant mental health component. However, these were not the subject matter of this review. The younger these children are, the more difficult is the systematic distinction between physical and mental health. This applies in particular for the age of early childhood (<3 years). Primarily family-oriented studies have to be used for information about this age, which is important for the later mental development.
When systemising the study types, not all potential sources of biases were considered (e.g. survey mode, response or drop-out rates) [63]. Furthermore, an established risk-of-bias tool was not used because, as in the case of the review on the adult population [15], systematic biases were the explicit object of the study question of this rapid review. Also, effect sizes were not considered, which is reserved for future monothematic meta-analyses. It was, however, the aim of this review, to provide a systematic, wide-ranging overview. Even if − for good reasons − the COVID-19 pandemic can be considered to be the relevant stressor for the mental health of children and adolescents, lockdown [34, 37, 47], but also the numerous spontaneous COVID-19-related additional surveys as part of long-term studies [23,28,35,36,38,45], the data acquisitions of which mainly took place at the beginning of the pandemic. This, however, is not unproblematic because effects on the mental health can be expected in particular in the case of chronicity of stressors, and the need for knowledge increases in the temporal course of the pandemic in this respect.

Limitations and strengths
The focus of this rapid review was on the changes in mental health of children and adolescents in the general population during the course of the pandemic. In contrast to the narrative review from 2020 [4], school-related aspects were only considered when a direct link with the mental health of children and adolescents during the pandemic was established in the publications. Even though health and the school situation of children and adolescents are closely linked, this link is not sufficiently represented in research. In particular, due to the repeated school closures in the course of the pandemic this focus would have been desirable with regard to the mental health of children and adolescents. With the exception of children and adolescents with attention deficit/hyperactivity disorders or eating disorders, no subpopulations were searched deliberately for the review, which is a limitation. Specific sociodemographic subpopulations (e.g. families with low parental education or with migration background), however, were considered, given that they were also considered in the included publications. Other groups, such as children and adolescents with a chronic disease or a disability (special health care needs, SHCN) were not addressed. This may 26 FOCUS their environment. Even though the initial perception of acute stress can be considered an adequate reaction to an extraordinary crisis-such as the COVID-19 pandemic-and resulting mental impairments at the symptomatic level are not identical with manifest mental disorders, the risk of developing a mental disorder increases to the extent that stress and overburdening situations last. Particularly in the light of the long-lasting unfavourable effects of mental health problems in childhood and adolescence [53, 64], the prevention of long-term mental and physical health problems and for promoting mental health in youth is advisable.
This rapid review showed that the scientific interest in the sequelae of the pandemic appears to be more limited for children and adolescents than for adults. The look at the number of ongoing data acquisitions since the beginning of the pandemic revealed a lack of studies on the development of the mental health of children in the course of the pandemic from the first wave to 19.11.2021. In fact, the COPSY study is the only repeatedly conducted primary data collection on a nationally representative basis that comprised a comparatively broad spectrum of standardised and validated indicators and held a specific focus on the mental health of children and adolescents of a broad age spectrum. All other studies -including the studies of types A-D with a methodologically sound database -have relevant limitations in various respects, be it with regard to the sampling coverage (e.g. only certain age cohorts or only locally or regionally limited suitability for representative statements), with regard to the used indicators (e.g. use of predominantly non-standardised single items or the use of only few validated indicators, respectively) or with regard to their study focus (not primarily on mental health). specific health trends, which already existed before the pandemic, were neither empirically demarcated from time trends during the pandemic nor discussed in most of the publications. The reported time trends can thus not be interpreted as being caused by the pandemic. Indeed, the results of the nationwide KiGGS long-term study rather suggested prevalence declines rather than increases of population-based mental health problems and disorders among children and adolescents in the decade before the pandemic [53]. Moreover, the mental health of children and adolescents is influenced by many further factors, which in part may interact with the pandemic situation so as to increase to reduce risks (e.g. the family situation). The effects of such interactions, however, are not the subject matter of this review. According to our best knowledge, this rapid review provides the first systematic evidence synthesis of pandemic-related population-based results on the the mental health of children and adolescents in Germany, which can be considered a relevant strength on this review. Additional strengths are the systematic, multi-perspective view on the potential biases and the critical evaluation there of and-based on the comparable methodo logical approach-, as well as the comparability with the results of the rapid review for the adult population [15].       Online survey: Survey of parents and an associated child between 10 and 17 years (n=1.005). Representative population survey on behalf of the DAK-Gesundheit. The determination of the group of parents or guardians to be surveyed was made via a screening as part of the online panel forsa.ominet.

Data extraction results
Observational period: 07.05.2020 -14.05.2020 [34] DAK-Gesundheit (2020) a Wellbeing of the child compared to before the school closure Single item (parents' report), scale from 1 'significantly better' to 5 'significantly worse' than before the pandemic Decline of the wellbeing (worse or significantly worse) according to parents' report among 38%, increase (better or significantly better) among 21% [34].
Single item (self-reported), scale from 1 'significantly better' to 5 'significantly worse' than before the pandemic Decline of the wellbeing (worse or significantly worse) according to selfreport among 29%, increase (better or significantly better) among 31%.

SPATZ Health Study
Survey study (written questionnaires): Birth cohort study 2012 with n=362 as comprehensive survey from the maternity clinic in Ulm, which was the only one at that time (response rate 49%). The sample comprises all children of the follow-up examination among 6-and 7-year-olds of the SPATZ study, for which a questionnaire was completed in the first grade. Compared in cross-sectional analysis, children between 6 and 7 years were divided into four groups, which, before the first school closure in Germany (≤ 15 March 2020) were in first grade (groups 1-3), as well as the children, who were in first grade (group 4) during the pandemic (>15 March 2020).

Observational period:
March-May 2020 Corona stress questionnaire parents (CBB-E; parents' report) Medical clinic sample: Increase of the total stress among a total of 72% (strong: 23.6%, somewhat: 48.4%) of the children and adolescents according to parents' report, among 16.1% unchanged, among 11.8% declines of the stress (somewhat: 10.6%, strongly:

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Study type C: One-time comprehensive survey or one-time cross-sectional study, based on a sample drawn randomly from a reference population or an access panel or a populationrepresentative quota sampling Study/data basis and publications (including observational period etc.)

Study by the TU Munich and the Leibniz Institute for Economic research in Essen
Online survey: Study with n=3,818 women between 18 and 65 years, in a partnership, on experiences of violence during the pandemic, women with children n=1,474 of it. Quota sampling from pool of 100,000 survey-ready individuals of a private survey institute. Quotas were applied in terms of German state, age, net household income, education, employment status, and household size, in order to ensure the representativeness of the sample. List experiment for the survey of, e.g., severe physical violence against children.
Prevalence for severe physical violence against children in the last month at 1.97% [50].

Prevention radar of the Institute for Therapy and Health Research (IFT-Nord) on behalf of the DAK
Online survey: Pupils from 897 classes (n=14,287). A total of n=4,271 fifth and sixth graders, n=5,259 seventh and eighth graders, and n=4,757 ninth and tenth graders from 13 federal states were surveyed. A comprehensive survey of the respective grades took place. Proportion of the female respondents 49%, average age 13.0 years. Weighted by age, sex, and school type. c Mental health problems SDQ, subscale emotional problems) Risk factors for increased perceived stress were financial worries, increased perceived stress of a parent, procrastination, limited access to emotion regulation strategies and staying home during the lockdown.

TRANS-GEN study
Online survey: Mothers with children between 5 and 7 years (n=73) from a birth cohort started in 2013 by the maternity clinic in Ulm with three waves (t0 to t3) with 158 completed motherchild dyads with complete data sets from all three survey waves.  Over 50% of the children and adolescents are rather or significantly stressed, irritated, or lonely in 2020 [37].

Study: Being a child in times of Corona
Online survey: Survey of parents of children between 3 and 15 years, who were recruited as convenience sample using the snowball method; n=12,628 More negative parent-child interactions as well as less positive affect from parents and children, and higher negative affect from the children, but no higher negative affect from the parents on days when the children had to do schoolwork. Also days, on which the parents were integrated more strongly into the learning (i.e. the children worked less independently) with more negative parent-child interactions, less positive affect from the parents and children, and more negative affect among parents and children  Anonymised analysis of the nationwide data of the children between 0 and 12 years with KBV statutory health insurance in Germany with at least one doctor's visit between January 2019 and June 2020. 2019: n=8.29 million; 2020: n=8.5 million.
Analysis of the frequency of selected ICD-10-diagnosis groups, including F00-F99 (mental and behavioural disorders).

DAK Kinder-und Jugendreport 2021
Data basis: Anonymised billing data from n=760,023 children and adolescents up to the age of 17 years, who are ensured with the DAK-Gesundheit. The hospital treatments 2019 and 2020 were compared as well as the hospital treatments between spring and fall/winter lockdown in 2020.

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Care-related primary data Study type C One-time comprehensive survey or one-time cross-sectional study, based on a sample drawn randomly from a reference population or an access panel or a populationrepresentative quota sampling Study/data basis and publications (including observational period etc.)

Data extraction results Outcome
Indicator Result Project 'Youth welfare and social changes' at the German Youth Institute (DJI).
Online survey: Nationwide online comprehensive survey of all 575 youth welfare offices in Germany by the German Youth Institute, n=371 youth welfare offices participated (participation rate 65%). The project has been acquiring and analysing data on the situation and development of child and youth welfare since 1992.